System For Recycling Printed Circuit Boards

ABSTRACT

A process for recycling printed circuit boards includes pyrolyzing a number printed circuit boards to from an ash. Metals form the circuit boards are separated from the ash by density separation techniques. The metals are formed into a slurry electrode. The slurry electrode and a deposition electrode are placed in an electrolyte bath and the metals are electrorefined to form bars of metal. The slurry electrode is made by combining powderized metals with carbon powder and an ionic liquid to form an electrode paste. The electrode paste is placed inside a container with a screen to form the slurry electrode.

RELATED APPLICATIONS

The present invention claims priority on provisional patent application, Ser. No. 61/128561, filed on May 22, 2008, entitled “Printed circuit board Recycling Process” and is hereby incorporated by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

This invention was made in the performance of a Cooperative Research and Development Agreement with the Department of the Air Force. The Government of the United States has certain rights to use the invention

THE NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT

Not Applicable

REFERENCE TO A SEQUENCE LISTING, A TABLE, OR A COMPUTER PROGRAM LISTING

Not Applicable

BACKGROUND OF THE INVENTION

The fast pace of product life cycles in the electronics and computer industry results in large amounts of obsolete electronic products. These electronic products represent a landfill problem. These products often have heavy metals that can seep into ground water and contaminate water supplies. Recent legislation in Europe, China and several US states now mandate that in the near future electronics' manufactures must to take back their products at the end of the products life. In addition, the stringent rules of many landfills no longer allow these products to be thrown away. One of the main problems in recycling electrical and electronics products is the circuit boards. The circuit boards and their components have most of the heavy metals and may contain lead, mercury, cadmium and chromium. All of which are being strictly regulated. Presently, the only way to separate and extract these metals is to expose the circuit board to high temperatures until the metals vaporize and then the specific heavy metal can be separated and recovered. Unfortunately, this process is expensive, requires a tremendous amount of energy and introduces toxic off gasses into the atmosphere.

Thus there exists a need for a process for recycling circuit boards.

BRIEF SUMMARY OF INVENTION

A process for recycling printed circuit boards includes pyrolyzing a number printed circuit boards to from an ash. Metals from the circuit boards are separated from the ash by density separation techniques. The metals are formed into a slurry electrode. The slurry electrode and a deposition electrode are placed in an electrolyte bath and the metals are electrorefined to form bars of metal.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a block diagram of a process of recycling printed circuit boards in accordance with one embodiment of the invention;

FIG. 2 is a cross sectional view of an electrorefining bath in accordance with one embodiment of the invention;

FIG. 3 is a flow chart of the steps used in a process of recycling printed circuit boards in accordance with one embodiment of the invention; and

FIG. 4 is a is a flow chart of the steps used in a process of electrorefining a group of metals in accordance with one embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

A process for recycling printed circuit boards includes pyrolyzing a number printed circuit boards to from an ash. Metals form the circuit boards are separated from the ash by density separation techniques. The metals are formed into a slurry electrode. The slurry electrode and a deposition electrode are placed in an electrolyte bath and the metals are electrorefined to form bars of metal.

FIG. 1 is a block diagram of a process 10 of recycling printed circuit boards in accordance with one embodiment of the invention. The process 10 starts with printed circuit boards (PCBs) 12 undergoing pyrolysis 14. The pyrolysis machine 14 requires energy 16 and has outputs of crude oil 18, and flame retardants 20. The crude oil 18 can be reused as fuel oil or as feedstock. The flame retardant 20 can either be disposed of safely or reused. The carbon 22 can be added to fertilizer or safely land filled. The other output of the pyrolysis 14 is an ash containing metals and silica 24 and carbon 22. The ash is ground and density separated 26. The density separation 26 results in silica 28 which may be sold to a cement plant, carbon which can be safely land filled and metals 30 in a powdered form. The powdered metals 30 are combined with an ionic liquid 32 to form a solution 34. The solution 36 then is electrorefined 38 and results in pure metals 40. In one embodiment, the ionic liquid may be a choline chloride based ionic liquid consisting choline chloride and ethylenge glycol in a molar ratio of 1:2.

FIG. 2 is a cross sectional view of an electrorefining bath 50 in accordance with one embodiment of the invention. The bath 50 includes a slurry electrode 52 formed from a paste of powderized metals, carbon powder and an ionic liquid to form an electrode paste 54. The electrode paste 54 is placed in an electrode, container having a screen 56. The screen may be a filter paper that allows ions of the metal to pass freely through the filter paper. The slurry electrode 52 is placed next to a deposition electrode 58. The deposition electrode 58 is place vertically above the slurry electrode 52. The electrodes 52, 58 are in electrolytic bath 60 containing an ionic liquid 62 which covers the electrodes 52, 58. A voltage source 62 is connected to the electrodes 52, 58.

In operation, the slurry electrode will contain many metals, such as copper, zinc and silver. The deposition electrode will be formed of the metal that has the lowest oxidation reduction potential, for example copper. The voltage will be increased until a current starts to flow. This results in the copper in the slurry electrode 52 being plated onto the deposition electrode 58. Once all the copper in the slurry electrode 52 is removed, the copper deposition electrode will be removed. Next a zinc electrode will be used as the deposition electrode. This is because the oxidation reduction potential of zinc is less than that of silver. The voltage is increased until current starts to flow. This results in the zinc in the slurry electrode being plated onto the deposition electrode 58. Once all the zinc is removed, the process is repeated for the silver using a silver electrode.

FIG. 3 is a flow chart of the steps used in a process of recycling printed circuit boards in accordance with one embodiment of the invention. The process starts, step 70, by pyrolyzing the plurality of printed circuit boards to form an ash, step 72. The metals are separated from the ash at step 74. At step 76 the metals are electrorefined to form pure metal bars at step 78.

FIG. 4 is a is a flow chart of the steps used in a process of electrorefining a group of metals in accordance with one embodiment of the invention. The process starts, step 90, by combining metal powders with carbon powder to form an electrode powder at step 92. The electrode powder is mixed with an ionic liquid to form an electrode paste at step 94. The electrode paste is placed in a holder to form a slurry electrode at step 96. A deposition electrode is placed next to the slurry electrode in an electrolytic bath at step 98. At step 100, a voltage is applied between the slurry electrode and the deposition electrode, which ends the process at step 102.

While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alterations, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alterations, modifications, and variations in the appended claims. 

1. A process for recycling printed circuit boards, comprising the steps of: pyrolyzing a plurality of printed circuit boards to form an ash; separating a plurality of metals from the ash; and electrorefining the plurality of metals, to form a plurality of pure metal bars.
 2. The process of claim 1, wherein the step of electrorefining includes the step of creating a slurry electrode.
 3. The process of claim 2, wherein the step of creating a slurry electrode includes mixing the plurality of metal with a carbon powder to form a electrode powder.
 4. The process of claim 3, further including the steps of mixing the electrode powder with an ionic liquid to form an electrode paste.
 5. The process of claim 4, further including the steps of placing the electrode paste in an electrode container having a screen.
 6. The process of claim 1, wherein the step of electrorefining includes the steps of creating an ionic liquid of choline chloride ethylene glycol.
 7. The process of claim 1, wherein an anode and a cathode of the electrorefining step are stacked vertically.
 8. A process for electrorefining a plurality of metals comprising the steps of: combining a plurality of metals in powder form with a carbon powder to form an electrode powder; mixing the electrode powder with an ionic liquid to form an electrode paste; placing the electrode paste in a holder to form a slurry electrode; placing a deposition electron next to the slurry electrode in an electrolyte bath; and applying a voltage between the slurry electrode and the deposition electrode.
 9. The process of claim 8, wherein the step of combining the plurality of metals in powder form includes the step of grinding the plurality of metals.
 10. The process of claim 8, wherein the step of applying the voltage includes the step of increasing the voltage until a current exceeds a predetermined threshold. 